Many applications utilize magnetorheological (MR) fluids, including smart actuation systems, such as dampers, clutches, and isolators. MR fluids may be composed of magnetizable particles suspended in a carrier. Under an external magnetic field, the particles form chains or fibrils that impede the motion of the fluid, causing the fluid to exhibit a high apparent viscosity and reach a solid-like state. The yield stress, representing the strength of an MR fluid when reaching the solid-like state, may depend on the strength of the external magnetic field applied. MR fluids may be used when rapid changes in elastic and damping properties are required to maintain control of a machine, such as a vehicle.
When MR-based devices are in an off-state for a period of time without periodic mixing of the fluid, the magnetizable particles may settle, and because they may still retain some magnetism, they may become tightly bound or clumped. This may lead to clogging of the device and degradation of system performance. Further, the properties of the fluid may be more unpredictable when the device returns to an on-state. Some MR fluids include surfactants, such as detergents, emulsifiers or other polymer coated nanoparticles, to reduce surface tension of the fluid and mitigate clumping. However, the presence of other particles or substances in the MR fluids may reduce the maximum magnetic saturation of a fluid and thus weaken an MR fluid's yield stress.